Add an istream class that wraps raw data buffer

libs/util/include/psemek/util/memory_stream.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <iostream>
+
+namespace psemek::util
+{
+
+	struct memory_istream
+		: std::istream
+	{
+		memory_istream(std::string_view data)
+			: b_(data)
+		{
+			rdbuf(&b_);
+		}
+
+	private:
+		struct buf
+			: std::streambuf
+		{
+			buf(std::string_view data)
+			{
+				char * p = const_cast<char *>(data.data());
+				setg(p, p, p + data.size());
+			}
+		};
+
+		buf b_;
+	};
+
+}